To be clear: you won’t be worse off for contributing to a retirement plan. They’ll just want to capture any untaxed income in their calculations, so in addition to asking for AGI, they’ll ask about any pretax retirement contributions or other untaxed income. If you contribute to a Roth it won’t be added back because it is not pretax. Employer contributions to SEP or solo 401k might not be considered at some schools.
As for business value, if this is a simple freelance or consulting type setup without inventories or much equipment, the value won’t be much and probably won’t affect aid much at all. Think about what you could get if you sell the business quickly.